An increase in steam turbine inlet temperatures provides improved overall efficiency with a reduce fuel cost and carbon footprint. Steam turbines thus must be able to withstand such higher steam temperatures without compromising the useful life of the rotor and other components. Materials that are more temperature resistant may be used in the construction of the rotor, but such materials may substantially increase the cost of the rotor components. High pressure, lower temperature steam also may be used as a coolant for the rotor, but the use of such a cooling flow also may increase the costs of the rotor while also degrading overall rotor performance. Moreover, there are parasitic costs involved in using downstream cooling flows.
There is thus a desire for an improved turbo-machine such as a steam turbine and the like that can adequately and efficiently cool the rotor and other components for an improved lifetime but with limited parasitic losses for improved performance.